The containment boom of the present invention is of the type, as exemplified by U.S. Pat. Nos. 4,295,755 and 4,752,393, which represents the prior art. In those patents there is disclosed a containment boom wherein an elongated flotation casing is held expanded in a condition of use by an elongated spiral coil extending substantially throughout the length of the boom. When the containment boom is wound on a drum the coil collapses in a predetermined direction, and when the boom is deployed from the spool the coil springs back to its spiral coiled condition. The flotation casing may also be segmented internally by partition walls which are secured to the casing and some of the spirals of the coil. Such containment booms have certain disadvantages in that they are difficult to repair when the coil spring becomes damaged. Also, they are also difficult to manufacture due to their long unitary coil construction. Furthermore, some of the casings use thick flotation blocks internally thereof to provide buoyancy. These booms also occupy irregular thick spaces on a reel when wound thereon. It is therefore not possible to store very long boom lengths, or else very large reels are necessary for its storage. A still further disadvantage of such prior art containment boom is that the boom is pulled onto the spool or reel by the ballast which is usually a chain secured to the bottom of a skirt. Accordingly, there is not a uniform pulling force across the boom when wound on the reel, and this causes irregularities in the boom stored on the reel which can lead to damage.